Operating mechanism for the movable contact of an air blast circuit breaker including means for slowing down the motion of the contact



Aug. i8, 197% o. p ssoN ETAL 3,524,954

OPERATING MECHANISM FOR THE MOVABLE CONTACT OF AN AIR BLAST CIRCUIT BREAKER INCLUDING MEANS FOR SLOWING DOWN THE MOTION OF THE CONTACT Filed May 15, 1967 Fig.2 C I Fig.3

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United States Patent 3,524,954 OPERATING MECHANISM FOR THE MOVABLE CONTACT OF AN AIR BLAST CIRCUIT BREAKER INCLUDING MEANS FOR SLOWIN G DOWN THE MOTION OF THE CONTACT Olof Eliasson, Ludvika, and Karl Gustav Sindahl, Sollentuna, Sweden, assignors to Allmiinna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Filed May 15, 1967, Ser. No. 638,294 Claims priority, application Sweden, May 27, 1966, 7,268/ 66 Int. Cl. Htllh 33/82 US. Cl. 200-148 Claims ABSTRACT OF THE DISCLOSURE An air blast circuit breaker has a container for air under pressure and a movable contact in the container driven by an operating piston moving in a cylinder; air under pressure can be admitted to one side of the cylinder to move the contact towards open position; a conduit connects the space on the other side of the cylinder to the container; to damp the movement of the contact, one of the piston and cylinder walls has a plate with an opening leading to the conduit while the other has a damping piston which moves into the hole to retard the flow of air through the conduit as the contact reaches a predetermined point, there is a second damping piston which enters the hole as the contact approaches fully open position; the plate is movable and has holes in its peripheral portion to allow freer flow of air during the return movement of the movable contact.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to an operating mechanism for the movable contact of an air blast circuit breaker and more specifically relates to an operating mechanism wherein the movable contact is temporarily slowed down in its motion toward its fully disengaged position at a distance from the cooperating stationary contact which is most favourable for are interruption.

The prior art The invention constitutes a particularly advantageous improvement of the air blast circuit breaker according to US. Pat. No. 3,118,996 of H. Forwald. This circuit breaker comprises a container permanently filled with compressed air, containing a main breaking gap having a movable contact provided with a blast air channel and joined to a piston. One side of the piston limits a first chamber which, by means of an operating valve, is connectable to the open air to close the main breaking gap or to the compressed air system of the container to open the main breaking gap. In order during the opening movement to be able to retard the movement of the movable contact of the main breaking gap at a distance from the stationary contact suitable for extinguishing the arc, the air blast circuit breaker is arranged so that the other side of the piston limits a compression chamber which, through a throttle means, is in permanent connection with the air blast system. The circuit breakers shown as examples in the said patent are provided with both throttle and non-return valves.

SUMMARY OF THE INVENTION In the arrangement according to the present invention, however, the desired eflfect can be achieved without such valves, which makes the device both simpler and safer in operation. The invention is characterised in that the throtice tle means comprises a damping piston which, when the movable contact has reached a favourable distance from the stationary contact for extinguishing the arc, is arranged to pass through a hole fitting the damping piston, so that the connection between the compression chamber and the compressed air system of the container is throttled during passage of the piston.

In the circuit breakers shown in the said patent the throttle means operates in such a way that when damping has commenced the means continues to retard (due to continued compression of the air behind the driving piston) during the entire remaining part of the movement of the movable contact. However, this means that it takes rather a long time before the movable contact reaches its final position. In order to avoid this the throttle means according to the invention is suitably arranged so that the connection between said compression chamber and the compressed air system is almost entirely free both before and after the period when the piston passes through the hole. This arrangement has the advantage that the damping piston can accelerate after damping and that final position of the movable contact is reached earlier. This in turn means that the blast-valve can be closed sooner and the breaker therefore needs less air.

In order to prevent the movable contact bouncing while taking up its open end-position, it is usually necessary to arrange some form of end position damping. However, the throttle means according to the present invention can easily be arranged also to take care of this damping. A suitable modification of the means for this purpose is obtained, for example, by means of a second damping piston arranged to be pushed into said hole when the movable contact nears its open end-position.

The hole fitting the damping piston(s) is most easily arranged in a so-called damping plate placed in connection with the compression chamber. This damping plate is preferably fastened so that it is axially displaceable so that it can be lifted from its seat when the circuit breaker is closed and thus expand the air passage between the compressed air system of the container and the compression chamber. The closing movement can thus take place without damping.

The damping piston is suitably supported by a piston rod which is adjustable in longitudinal direction. It is thus possible to adjust the time of damping to that point in the operation when the movable contact is at a favourable distance from the counter-contact for extinguishing the arc.

BRIEF DESCRIPTION OF DRAWINGS The invention will be further described with reference to the embodiments shown in the accompanying drawing. FIG. 1 shows a section through a circuit breaker according to the invention and FIG. 2 shows a section through the throttle means of the circuit breaker on a larger scale. FIG. 3 shows a section through another circuit breaker with an alternative embodiment of the throttle means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 'FIG. 1 shows a circuit breaker having a container 1 permanently filled with compressed air and built as a unit with a mechanism housing 2. In the container 1 is a main breaking gap containing a resilient stationary contact 3 and a movable contact 4, said contacts being connected to connection means 24- and 25, respectively by means of sliding contacts 22 and 23, respectively. The container 1 is supported by a hollow supporting insulator 26 which is arranged on an earthed base 27. The supporting insulator 26 also serves as the pneumatic connection between the container 1 and the lower part of the circuit breaker. Compressed air is supplied to the circuit breaker through a conduit'28 from a compressed 'air source, not shown. Inside the supporting. insulator 26 is arranged a control air insulator 29 which, through the conduit 30 and valve means, not shown, is fed from the same compressed air source. The movable contact 4 of the circuit breaker, which is provided with a blast air channel 9, is rigidly connected with a valve head 11 closing the blast air channel 9 in the completely open and completely closed positions of the main breaking gap. The valve head 11 is joined by means of a piston rod to a driving piston 6, one side of which limits a first chamber 8 and the other side a compression chamber 7. The chamber 7 is, through a conduit 13, in communication with the container 1 by means of a throttle means consisting of a damping piston 31 joined to the driving piston 6 and a damping plate 32 fitting the damping piston. The connection between the driving piston and damping piston is effected by a piston rod 33. From FIG. 2 it is clear that the damping plate 32 is attached with the help of a blocking ring 34 so that it is axially displaceable between two end positions. A number of eccentrically placed holes 36 are also arranged in the damping plate besides the hole 35 fitting the damping piston 31. The circuit breaker is also provided with a damping resistor 37 and a resistor breaking gap 38.

The circuit breaker is opened by supplying compressed air to the space 8 through the control air insulator 29. The movable contact 4 then starts to move rapidly to the right and the valve head 11 opens the blast air channel 9 so that compressed air for arcs which might arise at the main breaking gap can flow from the container 1 and out to the open air through the cooling grid 39. When the damping piston 31 reaches the damping plate 32, the movable contact is retarded due to the fact that the connection between the compression chamber 7 and the container 1 is throttled. During the passage of the damping piston through the damping plate, the play between piston and hole determines the contact speed. When the damp ing piston has passed through the damping plate, however, there is no longer any obstruction and the movable contact can again accelerate freely.

In order as far as possible to prevent the movable contact bouncing while taking up its open end-position the piston rod 33 is provided with another piston 40. This piston is positioned on the piston rod 33 so that, just before the rod has reached the end position piston 40 is pushed into the hole in the damping plate 32 and throttles this hole during the remaining part of the opening operation. When the piston 40 is inserted into the hole in the damping plate a compression pressure starts to act upon the back of the driving piston 6. This pressure continues to increase as the driving piston nears its end position so that its speed is retarded to such a low value that the driving piston can take up its rest position without bouncing.

The main breaking gap is closed by connecting the conduit 30 to the open air so that the space 8 is emptied and the driving piston 6 and the movable contact 4 are t 4 air container 1 is arranged as a central channel through a the piston rod- 5.

As is clear from the shown embodiments, it is possible by regulating the damping pressure by means of the play between a solid piston and the hole in a plate to obtain a throttle means which is extremely simple and robust. The practical use of the means is also increased since it can easily be made so that several damping operations can be obtained during one and the same movement.

We claim:

1. An air blast circuit breaker comprising a container permanently filled with compressed air supplied from a compressed air source, a main breaking gap disposed within said container, said breaking gap comprising a substantially stationary contact and a movable contact, an operating piston, said operating piston being connected to said movable contact, means forming a cylinder, said operating piston being disposed within said cylinder, said 2 operating piston dividing said cylinder into an operating pressed to the left. The closing movement takes place without any damping influence from the throttle means 31, 32. Should the air between the damping piston 31 and the plate 32 be compressed, the plate 32 is lifted from its seat so that the hole 36 is cleared and thus increases the air passage to the space'on the other side of the plate.

FIG. 3 shows a section through the mechanism housing 2 of another circuit breaker with an alternative embodiment of the throttle means. Thedamping pistons 31 and 40 are in this case attached by means of the piston rod 33 to the wall of the mechanism housing, while the damping plate 32 is axially displaceably attached in a notch in the driving piston 6. In this embodiment the connetcion 13 between the compression chamber 7 and the compressed chamber and a compression chamber, conduit means connecting said compression chamber to said container, means for selectively connecting said operating chamber to the open air for closing the main breaking gap or to said compressed air source for opening of the breaking gap, a throttle means for said conduit means, said throttle means comprising a damping piston and a damping plate, said damping plate having a hole leading to said conduit means and fitting said damping piston, said damping pistons being accommodated in said compression chamber and arranged to pass through said hole and thereby to throttle said conduit means when during a breaking operation said movable contact has reached a favorable interruption distance with respect to said stationary contact.

2. In an air blast circuit breaker according to claim 1, said conduit means permitting free communication between said compression chamber and said container both before and after the passage of said piston through said hole.

3. In an air blast circuit breaker according to claim 1, said throttle means including means to damp the movement of said movable contact in its open end position.

4. In an air blast circuit breaker according to claim 3, said damping means comprising a second damping piston, said second damping piston being arranged to be pushed into said hole when said movable contact nears its open end position.

5. In an air blast circuit breaker according to claim 4, said damping pistons being supported by the same piston rod.

6. In an air blast circuit breaker according to claim 1, a seat for said damping piston, said damping plate being axially displaceable from said seat and having an opening therein so positioned that, during a closing operation of the circuit breaker, it is cleared for the passage of air from said container to said compression chamber.

7. In an air blast circuit breaker according to claim 1, said damping plate being attached to said operating piston.

8. In an air blast circuit breaker according to claim 1, said damping piston being joined to said operating piston.

9. In an air blast circuit breaker according to claim 1, said damping piston being supported by a piston rod having adjustable length.

10. In an air blast circuit breaker according to claim 1, said damping piston being solid.

References Cited UNITED STATES PATENTS 1,696,604 12/1928 Hilliard 200-l50 3,118,996 1/1964 Forwald 200---148 ROBERT S. MACON, Primary Examiner 

